you are being such a great friend!
Some of the things I would say affect my social life/time with my friends the most are:
1. Side affects- your friends might be taking different medications for their crohns disease, some of which are likely to have side affects. This can mean they might be irritable at times, have mood swings, feel either drowsy or they can't sleep or they might even be feeling insecure about a change in appearance brought on by medication. It is important just to be aware and considerate of these things.
2. Food- Your friends might have to change their diet to facilitate foods that contain little fibre/sugar/ dairy or whatever foods they find affect them negatively. Keep their diet in mind when choosing places to visit/ eat or when buying presents on birthdays or christmas - aka you probably shouldn't buy them chocolates or sweets!
3. going out- If you are going out with your friends for example to a concert or a party, be aware that your friends might be anxious about the availability of bathrooms, particularly if they are experiencing a flare. This might mean that they have to go home early if they are feeling unwell and may not be able to stay over at a friends house. you can help them by visiting places where bathroom accessibility isn't a problem and going home with them afterwards if they need to go home. (btw, I am a college student so this scenario is very typical for me- staying at people's houses after a party may not be relevant to you!)
4. Energy- as the other replies have already said, your friends may have very little energy at times, try and facilitate this the best you can